U.S. patent application number 13/265014 was filed with the patent office on 2012-02-09 for rubber composition for conveyor belt, and conveyor belt.
This patent application is currently assigned to Bridgestone Corporation. Invention is credited to Hiroki Nakano.
Application Number | 20120034486 13/265014 |
Document ID | / |
Family ID | 43011094 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120034486 |
Kind Code |
A1 |
Nakano; Hiroki |
February 9, 2012 |
RUBBER COMPOSITION FOR CONVEYOR BELT, AND CONVEYOR BELT
Abstract
Disclosed is a rubber composition for a conveyor belt, which is
characterized by containing 0.5-3 parts by weight of zinc
dimethacrylate and 1.1-4.5 parts by weight of neodecanoic acid
cobalt boride per 100 parts by weight of the rubber component. Also
disclosed is a conveyor belt in which a galvanized steel cord that
is covered with an adhesive rubber layer formed from the rubber
composition is used as the core body. The rubber composition has
excellent adhesion to a galvanized steel cord and good
vulcanization rate. The conveyor belt using the rubber composition
has excellent durability and productivity.
Inventors: |
Nakano; Hiroki; (Kanagawa,
JP) |
Assignee: |
Bridgestone Corporation
Chuo-ku
JP
|
Family ID: |
43011094 |
Appl. No.: |
13/265014 |
Filed: |
April 19, 2010 |
PCT Filed: |
April 19, 2010 |
PCT NO: |
PCT/JP2010/056916 |
371 Date: |
October 18, 2011 |
Current U.S.
Class: |
428/608 ;
524/324; 525/149; 525/193; 525/245 |
Current CPC
Class: |
B29D 29/06 20130101;
B65G 15/36 20130101; C08L 7/00 20130101; C08K 3/38 20130101; C08L
7/00 20130101; C08J 5/00 20130101; C08L 21/00 20130101; C08L 9/06
20130101; C08L 9/06 20130101; C08L 61/04 20130101; C08K 5/098
20130101; C08L 9/06 20130101; C08J 2321/00 20130101; C08K 5/55
20130101; C08K 5/098 20130101; C08K 5/098 20130101; C08L 2666/02
20130101; C08K 5/098 20130101; C08L 2666/02 20130101; C08L 7/00
20130101; C08L 61/04 20130101; C08L 7/00 20130101; C08K 5/55
20130101; C08L 61/04 20130101; C08L 7/00 20130101; C08L 61/04
20130101; C08L 21/00 20130101; Y10T 428/12444 20150115; C08L 21/00
20130101 |
Class at
Publication: |
428/608 ;
525/245; 525/193; 525/149; 524/324 |
International
Class: |
B32B 7/12 20060101
B32B007/12; C09J 109/06 20060101 C09J109/06; B32B 15/02 20060101
B32B015/02; C09J 11/06 20060101 C09J011/06; C09J 4/02 20060101
C09J004/02; C09J 107/00 20060101 C09J107/00; C09J 161/06 20060101
C09J161/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2009 |
JP |
2009-101586 |
Claims
1. A rubber composition for conveyor belt which comprises
containing therein 0.5 to 3 parts by weight of zinc dimethacrylate
and 1.1 to 4.5 parts by weight of cobalt neodecanoate boride for
100 parts by weight of rubber component.
2. The rubber composition for conveyor belt as defined in claim 1,
in which the rubber component is composed of 20 to 70 parts by
weight of natural rubber and 80 to 30 parts by weight of synthetic
rubber such that their total amount is 100 parts by weight.
3. The rubber composition for conveyor belt as defined in claim 2,
in which said synthetic rubber is one or more species selected from
styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene
rubber (IR).
4. The rubber composition for conveyor belt as defined in claim 1,
which further contains 1 to 10 parts by weight of phenolic resin
for 100 parts by weight of the rubber component.
5. The rubber composition for conveyor belt as defined in claim 4,
in which the phenolic resin is one which contains internally added
hexamethylenetetramine.
6. The rubber composition for conveyor belt as defined in claim 1,
which further contains 1 to 10 parts by weight of .beta.-naphthol
for 100 parts by weight of the rubber component.
7. The rubber composition for conveyor belt as defined in claim 1,
which further contains 1 to 10 parts by weight of
hexamethoxymethylated melamine and/or hexamethylenetetramine as a
curing agent for 100 parts by weight of the rubber component.
8. A conveyor belt of the type composed of covering rubber layers
and a core of galvanized steel cords interposed between them which
is coated with an adhesive rubber layer, wherein said adhesive
rubber layer is formed from the rubber composition defined in claim
1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a rubber composition for
conveyor belt which excels in adhesion to galvanized steel cords
and has an adequate rate of galvanization both required for
efficient production of conveyor belts, and also to a conveyor belt
formed with the rubber composition.
BACKGROUND ART
[0002] Galvanized steel cords used as reinforcing materials used
for rubber compositions are most suitable for reinforcing materials
for conveyor belts reinforced with steel cords, working in a humid
environment on account of their excellent corrosion resistance.
Such galvanized steel cords are required to keep good adhesion to
rubber for an extended period of time under humid conditions so
that they ensure a long life for conveyor belts.
[0003] There have been proposed several methods for achieving good
adhesion between rubber and galvanized steel cords, which involve
incorporation of rubber component with rosin, an organic cobalt
salt, and an organic chlorine compound in combination (Patent
Document 1: JP-A 2006-312744), incorporation of rubber component
with any one of triazine, zinc dimethacrylate, and zinc diacrylate,
and an organic cobalt salt in combination (Patent Document 2: JP-A
2005-350491), or incorporation of rubber component with an
acid-modified polymer and zinc dimethacrylate in combination
(Patent Document 3: JP-A 2006-176580).
[0004] The foregoing conventional technologies permit improved
adhesion between rubber and galvanized steel cords but suffer the
disadvantage of decreasing in the rate of vulcanization owing to
the presence of organic cobalt salt and zinc dimethacrylate, which
is detrimental to mass production and productivity.
[0005] Consequently, there has been a demand of a new rubber
composition for conveyor belt which exhibits good adhesion to
galvanized steel cords and good durability in a severe working
environment under humid and hot conditions and has an adequate rate
of vulcanization which allows efficient mass production and
productivity of conveyor belts.
PRIOR ART DOCUMENTS
Patent Documents
[0006] Patent Document 1: JP-A 2006-312744 [0007] Patent Document
2: JP-A 2005-350491 [0008] Patent Document 3: JP-A 2006-176580
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0009] The present invention was completed in view of the
foregoing. It is an object of the present invention to provide a
rubber composition for conveyor belt and also to a durable conveyor
belt formed with the rubber composition. The rubber composition
excels in adhesion to galvanized steel cords and has an adequate
rate of vulcanization which allows efficient production of conveyor
belts.
Means for Solving the Problems
[0010] As the result of comprehensive researches for solution to
the above-mentioned problems, the present inventors found that not
only it is possible to improve adhesion between rubber and
galvanized steel cords but it is also possible to effectively
increase the rate of vulcanization of rubber, thereby allowing
efficient production of durable conveyor belts, if the organic
cobalt salt to be added to rubber in combination with zinc
dimethacrylate (for improved adhesion between rubber and galvanized
steel cords) is cobalt neodecanoate boride in an adequate amount.
This finding led to the present invention.
[0011] The present invention is directed to a rubber composition
for conveyor belt which contains 0.5 to 3 parts by weight of zinc
dimethacrylate and 1.1 to 4.5 parts by weight of cobalt
neodecanoate boride for 100 parts by weight of rubber component,
and also to a conveyor belt of the type composed of covering rubber
layers and a core of galvanized steel cords interposed between them
which is coated with an adhesive rubber layer, wherein the adhesive
rubber layer is formed from the rubber composition according to the
present invention.
[0012] The present inventors' continued researches revealed that
the rubber composition exhibits good adhesion if the rubber
component is composed of natural rubber and synthetic rubber such
as styrene-butadiene rubber (SBR) in an adequate ratio and also if
the rubber composition is incorporated with any of phenolic resin
particularly the one containing internally added
hexamethylenetetramine, .beta.-naphthol, and hexamethoxymethylated
melamine (curing agent).
[0013] Thus, the present invention covers the preferred embodiments
(1) to (7) specified below.
(1) The rubber composition for conveyor belt and the conveyor belt
formed therewith according to the present invention, wherein the
rubber component is composed of 1 to 10 parts by weight of natural
rubber and 80 to 30 parts by weight of synthetic rubber such that
their total amount is 100 parts by weight. (2) The rubber
composition for conveyor belt and the conveyor belt formed
therewith as defined in (1) above, wherein the synthetic rubber is
one or more species selected from styrene-butadiene rubber (SBR),
butadiene rubber (BR), and isoprene rubber (IR). (3) The rubber
composition for conveyor belt and the conveyor belt formed
therewith according to the present invention, which contains 1 to
10 parts by weight of phenolic resin for 100 parts by weight of the
rubber component. (4) The rubber composition for conveyor belt and
the conveyor belt formed therewith as defined in (4) above, wherein
the phenolic resin is the one which contains internally added
hexamethylenetetramine. (5) The rubber composition for conveyor
belt and the conveyor belt formed therewith according to the
present invention, which contains 1 to 10 parts by weight of
.beta.-naphthol for 100 parts by weight of the rubber component.
(6) The rubber composition for conveyor belt and the conveyor belt
formed therewith according to the present invention, which contains
1 to 10 parts by weight of hexamethoxymethylated melamine and/or
hexamethylenetetramine as a curing agent for 100 parts by weight of
the rubber component. (7) The conveyor belt of the type composed of
covering rubber layers and a core of galvanized steel cords
interposed between them which is coated with an adhesive rubber
layer, wherein the adhesive rubber layer is formed from the rubber
composition according to the present invention.
Advantageous Effects of the Invention
[0014] The rubber composition for conveyor belt according to the
present invention excels in adhesion to galvanized steel cords and
an adequate rate of vulcanization, both required for efficient
production of durable conveyor belts.
BRIEF DESCRIPTION OF DRAWING
[0015] FIG. 1 is a schematic sectional view showing the specimen
used for adhesion test in the example.
EMBODIMENT FOR CARRYING OUT THE INVENTION
[0016] The rubber composition for conveyor belt according to the
present invention is characterized in containing 0.5 to 3 parts by
weight zinc dimethacrylate and 1.1 to 4.5 parts by weight of cobalt
neodecanoate boride for 100 parts by weight of rubber
component.
[0017] The rubber component as the constituent of the rubber
composition according to the present invention may be any known one
that is used as the adhesive rubber layer for steel cords in
conveyor belts. It may be natural rubber or a mixture of natural
rubber and synthetic rubber.
[0018] Examples of the synthetic rubber are listed below.
Polyisoprene rubber (IP), polybutadiene rubber (BR), and
polychloroprene rubber, which are homopolymers of such conjugated
diene compounds as isoprene, butadiene, and chloroprene;
styrene-butadiene copolymer rubber (SBR),
vinylpyridine-butadiene-styrene copolymer rubber,
acrylo-nitrile-butadiene copolymer rubber, acrylic acid-butadiene
copolymer rubber, methacrylic acid-butadiene copolymer rubber,
methyl acrylate-butadiene copolymer rubber, and methyl
methacrylate-copolymer rubber, which are copolymers of the
above-mentioned conjugated diene compound with such vinyl compound
as styrene, acrylonitrile, vinylpyridine, acrylic acid, methacrylic
acid, alkyl acrylates, and alkyl methacrylates; copolymers [such as
isobutylene-isoprene copolymer rubber (IIR)] formed from olefins,
such as ethylene propylene, and isobutylene, and diene compounds;
copolymer (EPDM) of olefins and non-conjugated diene [such as
ethylene-propylene-cyclopentadiene terpolymer,
ethylene-propylene-5-ethylidene-2-norbornene terpolymer, and
ethylene-propyene-1,4-hexadiene terpolymer]; polyalkenamer [such as
polypentenamer] resulting from ring opening polymerization of
cycloolefin; rubber [such as polyepichlorohydrin rubber capable of
vulcanization with sulfur] which results from ring opening
polymerization of oxirane rings; and polypropyleneoxide rubber.
Additional examples include halides of the foregoing rubbers, such
as chlorinated isobutylene-isoprene copolymer rubber (Cl-IIR) and
brominated isobutylene-isoprene copolymer rubber (Br-IIR). Another
example is a ring-opening polymer of norbornene. The
above-mentioned rubbers may be used by blending with a saturated
elastomer such as epichlorohydrin rubber, polypropyleneoxide
rubber, or chlorosulfonated polyethylene. Incidentally, preferable
among the foregoing synthetic rubbers is styrene-butadiene
copolymer rubber (SBR).
[0019] The rubber component may be formed from the natural rubber
and the synthetic rubber in any ratio without specific
restrictions. The amount of the natural rubber is usually 20 to 70
parts by weight and preferably 20 to 50 parts by weight, and the
amount of the synthetic rubber is usually 80 to 30 parts by weight
and preferably 80 to 50 parts by weight, with their total amount
being 100 parts by weight.
[0020] According to the present invention, the rubber composition
for conveyor belt contains zinc dimethacrylate in an amount of 0.5
to 3 parts by weight, preferably 0.5 to 2 parts by weight, for 100
parts by weight of the rubber component mentioned above. Addition
of the zinc dimethacrylate is intended to improve adhesion to
galvanized steel cords. With an amount less than 0.5 parts by
weight, it does not improve adhesion as intended in the present
invention. With an amount more than 3 parts by weight, it results
in excessively slow vulcanization which is undesirable for rolling
performance and efficient production intended by the present
invention.
[0021] In addition, according to the present invention, the rubber
composition for conveyor belt contains cobalt neodecanoate boride
in an amount of 1.1 to 4.5 parts by weight, preferably 1.5 to 3.5
parts by weight, for 100 parts by weight of the rubber component
mentioned above. The addition of the cobalt neodecanoate boride
improves adhesion strength and increases the rate of vulcanization,
thereby compensating for the decrease in the rate of vulcanization
which is caused by the addition of the zinc dimethacrylate
mentioned above. With an amount of addition of the cobalt
neodecanoate boride less than 1.1 parts by weight, it does not
sufficiently increase the rate of vulcanization as intended by the
present invention, and with an amount more than 4.5 parts by
weight, it adversely affects adhesion properties that depend on
water resistance and thermal aging resistance.
[0022] According to the present invention, the cobalt neodecanoate
boride mentioned above may be used in combination with cobalt
stearate, so that the resulting rubber composition has adequate
tackiness for improved rolling performance. The amount of the
cobalt stearate is not specifically restricted. It is usually 0.5
to 4 parts by weight, preferably 0.5 to 2 parts by weight, for 100
parts by weight of the rubber component mentioned above. With an
amount less than 0.5 parts by amount, it does not fully produce the
effect of improving rolling performance by addition. With an amount
more than 4 parts by weight, it adversely affects adhesion
properties and tackiness, thereby deteriorating the step of bonding
together the layers of covering rubber. The term "rolling
performance" means processability for passing the kneaded rubber
composition through sheeting rolls, thereby making it into
belt-like rubber with a specific thickness and width.
[0023] The rubber composition according to the present invention
may contain a phenolic resin in an amount adequate for further
improvement in adhesion properties. Examples of the phenolic resin
include phenol-formaldehyde resin, resorcinol-formaldehyde resin
and cresol-formaldehyde resin, with the phenol-formaldehyde resin
being preferable. The phenolic resin may be a pure one or a
modified one such as natural resin-modified one and oil-modified
one. Unrestrictive examples of the modified phenolic resin include
the one with internally added hexamethylenetetramine (hexamine) or
hexamethoxymethylated melamine (HMMM), which is preferable for
improvement in adhesive properties, with the former being
particularly desirable.
[0024] The phenolic resin may be added in any amount without
specific restrictions. However, it should be added in an amount of
1 to 10 parts by weight, preferably 1 to 5 parts by weight, for 100
parts by weight of the rubber component. With an amount less than 1
part by weight, it does not fully produce its effect. With an
amount more than 10 parts by weight, it adversely affects the
physical properties of the rubber compound, which leads to sticking
to the kneading machine and poor rolling performance, ending up
with an increased production cost. Two or more phenolic resin may
be used.
[0025] For further improvement in adhesion strength, the rubber
composition may be incorporated with a hydroxyl group-containing
monocyclic aromatic compound such as resorcinol or a hydroxyl
group-containing polycyclic aromatic compound such as
.beta.-naphthol, with the latter being preferable. The amount of
these compounds is not specifically restricted. It is usually 1 to
10 parts by weight, particularly 1 to 5 parts by weight, for 100
parts by weight of the rubber component. With an amount less than 1
part by weight, it does not fully produce its effect. With an
amount more than 10 parts by weight, it deteriorates the physical
properties of the rubber composition and it is wasted
uneconomically. Incidentally, the .beta.-naphthol should preferably
be used in combination with hexamethoxymethylated melamine and/or
hexamethylenetetramine as a curing agent which is mentioned
later.
[0026] The rubber composition may also be incorporated with a
curing agent for its further improvement in adhesion strength. The
curing agent is a methylene donor, such as hexamethylenetetramine
and methylolated melamine derivative, with the latter including
hexamethylolated melamine, hexamethoxymethylated melamine,
hexaethoxymethylated melamine,
N,N',N''-trimethyl-N,N',N''-trimethylolated melamine,
N,N',N''-trimethylolated melamine, N-methylolated melamine,
N,N'-di(methoxymethylated)melamine and
N,N',N''-tributyl-N,N',N''-trimethylolated melamine. Preferable
among these examples is either or both of hexamethoxymethylated
melamine or hexamethylenetetramine, and they should preferably be
used in combination with the .beta.-naphthol mentioned above.
[0027] The curing agent may be used in any amount without specific
restrictions. Usually it is used in an amount of 1 to 10 parts by
weight, particularly 1 to 4 parts by weight, for 100 parts by
weight of the rubber component. With an amount less than 1 part by
weight, it does not fully produce its effect. With an amount more
than 10 parts by weight, it is detrimental to the rubber properties
and is wasted uneconomically.
[0028] The rubber composition of the present invention is usually
incorporated with sulfur, organic sulfur compound, and any other
vulcanizing agent in an unrestricted amount of 1 to 10 parts by
weight, preferably 2 to 5 parts by weight, for 100 parts by weight
of the rubber component. The vulcanizing agent may be used in
combination with a vulcanization accelerator, such as zinc oxide
and stearic acid, in an unrestricted amount of 1 to 20 parts by
weight, preferably 3 to 15 parts by weight, for 100 parts by weight
of the rubber component.
[0029] In addition, the rubber composition of the present invention
may be incorporated with a variety of oils including paraffinic,
naphthenic, or aromatic process oil, ethylene-.alpha.-olefin
cooligomer, mineral oil such as paraffin wax and fluid paraffin,
and vegetable oil such as castor oil, cotton seed oil, linseed oil,
rapeseed oil, soybean oil, palm oil, coconut oil, and peanut oil.
Preferable among these examples is aromatic process oil (aromatic
oil). They are added in an unrestricted amount of 1 to 10 parts by
weight, preferably 2 to 7 parts by weight, for 100 parts by weight
of the rubber component. The rubber composition may also be
incorporated with a filler, such as carbon black, silica, calcium
carbonate, calcium sulfate, clay, and mica, in an adequate amount
according to its intended use. Of these fillers, carbon black is
particularly desirable.
[0030] The rubber composition of the present invention may
optionally be incorporated with a variety of additives for rubber
according to need in an amount not harmful to the object of the
present invention. Such additives include vulcanization accelerator
such as sulfenamide, age resistor, wax, antioxidant, foaming agent,
plasticizer, lubricant, tackifier, and UV absorber.
[0031] The rubber composition for conveyor belt according to the
present invention can be firmly bonded to galvanized steel cords
when vulcanized in close contact with them. In practice, this is
accomplished by heating under pressure two sheets of the rubber
composition holding galvanized steel cords between them. Thus, the
rubber composition can be bonded to and cover the galvanized steel
cords. The condition of vulcanization varies depending on the
vulcanizer and accelerator selected. Vulcanization with sulfur may
be carried out at 135 to 180.degree. C. for 10 to 100 minutes.
[0032] The conveyor belt formed with the rubber composition
according to the present invention is not specifically restricted
in its structure. It is usually constructed of a core layer and
covering rubber layers holding it between them. The core layer
includes galvanized steel cords and the rubber composition of the
present invention holding them therein. The galvanized steel cords
and the covering rubber layers are not specifically restricted in
form and composition, respectively. Any known form and composition
may be properly selected according to the use of the conveyor
belt.
EXAMPLES
[0033] The invention will be described below in more detail with
reference to Examples and Comparative Examples, which are not
intended to restrict the scope thereof. The terms "parts" and "%"
used in the examples imply "parts by weight" and "wt %,"
respectively.
Examples 1 to 13 and Comparative Examples 1 to 13
[0034] These examples are designed to produce samples of rubber
compositions according to the formulation shown in Tables 1 and 2
given below and then test them for adhesion to galvanized steel
cords, rate of vulcanization, rolling performance, and laminating
performance. The results are shown in Tables 1 and 2.
[0035] The components shown in Tables 1 and 2 are commercial
products whose sources and trade names are listed below. [0036]
Natural rubber: RSS #3 [0037] Styrene-butadiene rubber: JSR Corp.,
"SBR 1500" (SBR produced by emulsion polymerization) [0038] Carbon
black: Asahi Carbon Co., Ltd., "#70" [0039] Age resistor: Sumitomo
Chemical Co., Ltd., "ANTIGENE 6C" [0040] Aromatic oil: Idemitsu
Kosan Co., Ltd., "Diana Process Oil AH-85" [0041] Sulfur: Tsurumi
Chemical Industry Co., Ltd., "Z Sulfur" [0042] Vulcanization
accelerator: Ouchi Shinko Chemical Industrial Co., Ltd., "Nocceler
NS-F" [0043] Zinc oxide: Toho Zinc Co., Ltd., "Ginrei SR" [0044]
Zinc dimethacrylate: Kawaguchi Chemical Industry Co., Ltd., "Actor
ZMA" [0045] Cobalt neodecanoate: DIC Corporation, "Cobalt
Versatate" [0046] Cobalt neodecanoate boride: DIC Corporation,
"DICNATE NBC II" [0047] Cobalt naphthenate: DIC Corporation,
"Cobalt naphthenate" [0048] Cobalt stearate: DIC Corporation,
"Cobalt Stearate" [0049] Phenolic Resin-1: Sumitomo Bakelite Co.,
Ltd., "Sumilite Resin PR 50235" [0050] Phenolic Resin-2 (with
internally added hexamethylenetetramine): Sumitomo Bakelite Co.,
Ltd., "Sumilite Resin PR-12687" [0051] .beta.-Naphthol: Mitsui Fine
Chemical Inc., "2-naphthol" [0052] Hexamethoxymethylated melamine:
Nihon Cytec Industries Inc., "CYREZ964RPC"
(1) Adhesion Test
[0053] a. Preparation of Specimens
[0054] The rubber composition for each Example was prepared by
kneading the components shown in Tables 1 and 2 all at once in a
Bumbary mixer. The resulting rubber composition was made into a
sheet (15 mm thick). A galvanized steel cord (7 mm in diameter) was
sandwiched by a pair of sheets, and the resulting assembly was
heated under pressure for vulcanization at 170.degree. C. for 40
minutes. Thus there was obtained the specimen for test.
[0055] b. Initial Adhesion Strength
[0056] The specimen was tested for adhesion strength by measuring
the power required for the galvanized steel cord to be pulled out
from it. This test accords with DIN 2231. The results of the test
are expressed in terms of index, with the value in Comparative
Example 4 being 100. The adhesion strength is proportional to the
index value.
[0057] c. Adhesion Strength after Heat Aging
[0058] The same test as above was repeated for the specimen which
had experienced heat aging at 145.degree. C. for 300 minutes under
pressure (2 MPa) exerted by a press.
[0059] d. Adhesion Strength after Moisture Absorption
[0060] The same test as above was repeated for the specimen which
had been allowed to stand at 70.degree. C. and 95% RH for 90
days.
(2) Rate of Vulcanization
[0061] The specimen was tested for the rate of vulcanization at
155.degree. C. in cure time of Tc(90) according to JIS K6300-2 by
using "Curelastometer, type W" made by Nichigo Shoji Co., Ltd. The
results of the test are expressed in terms of index, with the value
in Comparative Example 4 being 100. The smaller the measured value
of Tc(90), the larger the index value.
(3) Rolling Performance
[0062] A sample weighing 500 g, which was taken from the rubber
composition (unvulcanized), underwent rolling for three minutes on
"RII-2CC" (made by Kodaira Seisakusho Co., Ltd.) so that it was
made into a 3 mm thick sheet. During rolling operation, the sample
was examined for its tackiness to the roll surface. The tackiness
was rated as good (.circleincircle.), fair (.largecircle.), and
poor (x).
(4) Laminating Performance
[0063] The test for laminating performance was performed on an
unvulcanized rubber laminated body as a specimen simulating the
conveyor belt as shown in FIG. 1, which was produced in the
following manner. First, a rubber composition based on the
formulation shown below was prepared by kneading in a Bumbary
mixer. This rubber composition was made into the covering sheet 1
(4 mm thick). Then, each of the rubber compositions prepared
according to the formulations shown in Tables 1 and 2 was made into
the adhesion rubber layer 2 (2 mm thick). Two pieces of the
adhesion rubber layer 2 were placed on top of the other, with the
galvanized steel cords 3 (4 mm in diameter) interposed between
them. The resulting laminate product was held between two pieces of
the covering sheet 1, and the resulting assembly was pressed by a
hand roller so that the individual layers are bonded together.
(Formulation for Covering Rubber Composition)
TABLE-US-00001 [0064] Natural rubber (RSS #3) 70 pbw
Styrene-butadiene rubber (SBR 1500, from JSR Corp.) 30 pbw HAF
carbon 55 pbw Stearic acid (Kao Corp., "LUNAC RA") 2 pbw ZnO 3 pbw
Wax (Ouchi Shinko Chemical Industrial Co., Ltd., 2 pbw "Sunnoc N")
Age resistor RD (Kawaguchi Chemical Industry Co., Ltd., 0.5 pbw
"Antage RD") Age resistor 6C (Kawaguchi Chemical Industry Co.,
Ltd., 0.5 pbw "Antage 6C") Aromatic oil (Idemitsu Kosan Co., Ltd.,
"Diana Process Oil 5 pbw AH-85") Sulfur 2 pbw Vulcanization
accelerator (Ouchi Shinko Chemical Industrial 0.7 pbw Co., Ltd.,
"Nocceler NS-F")
[0065] Each specimen thus obtained was peeled off by force at the
interface between the covering rubber layer and the adhesion rubber
layer. The adhesiveness of the layers was rated as good
(.largecircle.) and poor (.DELTA.) depending on whether they have
sufficient bond strength or not.
TABLE-US-00002 TABLE 1 Comparative Comparative Example Ex. Example
Example 1 2 3 4 1 5 6 2 3 4 5 6 7 8 Formulation Natural rubber 40
40 40 40 40 40 40 40 40 40 40 40 40 40 (parts by Styrene-butadiene
60 60 60 60 60 60 60 60 60 60 60 60 60 60 weight) rubber Carbon
black 60 60 60 60 60 60 60 60 60 60 60 60 60 60 Age resistor 2 2 2
2 2 2 2 2 2 2 2 2 2 2 Aromatic oil 5 5 5 5 5 5 5 5 5 5 5 5 5 5
Sulfur 3 3 3 3 3 3 3 3 3 3 3 3 3 3 Vulcanization 1 1 1 1 1 1 1 1 1
1 1 1 1 1 accelerator Zinc oxide 15 15 15 15 15 15 15 15 15 15 15
15 15 15 Zinc dimethacrylate 2 2 2 2 2 2 2 2 2 2 2 2 Cobalt
neodecanoate 4 4 Cobalt neodecanoate 2.5 2.5 2.5 2.5 1.5 3.5 4.5
2.5 boride Cobalt naphthenate 5.8 Cobalt stearate 6.1 1 Phenolic
resin-1 3 Phenolic resin-2 3 3 3 3 3 3 (with internally added
hexamine) .beta.-naphthol 2 2 2 2 2 Hexamethoxymethylated 5 5 5 5 5
melamine Performance Initial adhesion 10 20 90 100 100 93 85 105
112 120 109 116 110 119 Test strength Adhesion strength 8 22 60 100
104 90 86 104 109 129 110 122 107 127 after heat aging Adhesion
strength 9 25 30 100 103 84 78 107 115 138 109 127 108 136 after
moisture absorption Rate of vulcanization 110 90 110 100 120 104
102 120 120 120 110 125 128 120 (Curelastometer T90 at 150.degree.
C.) Rolling performance .circleincircle. .largecircle.
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TABLE-US-00003 TABLE 2 Com. Ex. Example Comparative Example 7 9 10
11 12 13 8 9 10 11 12 13 Formulation Natural rubber 40 40 40 40 40
40 40 40 40 40 40 40 (parts by Styrene-butadiene 60 60 60 60 60 60
60 60 60 60 60 60 weight) rubber Carbon black 60 60 60 60 60 60 60
60 60 60 60 60 Age resistor 2 2 2 2 2 2 2 2 2 2 2 2 Aromatic oil 5
5 5 5 5 5 5 5 5 5 5 5 Sulfur 3 3 3 3 3 3 3 3 3 3 3 3 Vulcanization
1 1 1 1 1 1 1 1 1 1 1 1 accelerator Zinc oxide 15 15 15 15 15 15 15
15 15 15 15 15 Zinc dimethacrylate 2 2 2 2 2 2 2 2 0.3 7 2 2 Cobalt
neodecanoate 4 2 1.5 8 Cobalt neodecanoate 1.25 2.5 2.5 2.5 2.5 1 5
2.5 2.5 boride Cobalt naphthenate Cobalt stearate 1 1 0.5 2 0.1 3
Phenolic resin-1 Phenolic resin-2 3 3 3 3 3 3 3 3 3 3 3 3 (with
internally added hexamine) .beta.-naphthol 2 2 2 2 2 2 2 2 2 2 2 2
Hexamethoxymethylated 5 5 5 5 5 5 5 5 5 5 5 5 melamine Performance
Initial adhesion 120 119 118 113 118 103 98 102 97 105 97 103 Test
strength Adhesion strength 124 128 128 112 128 98 99 80 70 110 96
75 after heat aging Adhesion strength 130 133 138 109 137 92 89 75
35 120 85 70 after moisture absorption Rate of vulcanization 100
110 120 120 120 115 105 130 125 85 102 107 (Curelastometer T90 at
150.degree. C.) Rolling performance .circleincircle.
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[0066] It is apparent from Tables 1 and 2 that the rubber
composition for conveyor belt according to the present invention
exhibits good adhesion to galvanized steel cords and achieves
vulcanization at an adequate rate, so that it firmly adheres to
galvanized steel cords without retarding the rate of vulcanization,
and hence it permits efficient production of durable conveyor
belts.
EXPLANATION OF REFERENCE NUMERALS
[0067] 1 Covering rubber layer [0068] 2 Adhesive rubber layer
[0069] 3 Galvanized steel cords
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